This invention relates to continuously variable transmissions and particularly to hydromechanical mechanical transmissions and controls.
This invention relates to applicant's copending application Ser. No. 759,800, concurrently filed Jan. 17, 1977.
This invention provides a continuously variable ratio transmission of wide ratio coverage having a continuously variable transmission unit and a multistep ratio gear transmission or mechanical unit connected in series for extending the mechanical unit ratio range capability in a continuously variable overall ratio range. The continuously variable ratio unit has a planetary gearing portion dividing input torque and transmitting torque to its output member in a constant torque ratio mechanical path, and a continuously variable portion connecting the reaction and output members of the planetary gearing portion and transmitting torque in a continuously variable ratio torque path. In the continuously variable unit, the continuously variable portion controls the reaction member speed of the gearing portion to, in a reaction phase, decrease the reaction direction speed from a high value to zero to increase the continuously variable unit speed ratio from zero to the stationary reaction speed ratio, and in an action phase increase action direction speed, which is opposite to reaction direction speed, to further increase the continuously variable unit speed ratio to a maximum value. The percent power transmitted in the continuously variable hydraulic path varies from 100% through 0% and then to a low percent and in the mechanical path inversely varies from 0% through 100% and then to a high percent as continuously variable unit speed ratio varies from zero speed ratio through the stationary reaction speed ratio to maximum speed ratio. When the mechanical unit is in first gear ratio, the continuously variable unit is controlled for progressive continuously variable speed ratio changes from zero speed ratio at vehicle stall, through the stationary reaction speed ratio to the maximum in 1st gear, which is the first step-up speed ratio, and a similar progressively continuously changing overall transmission speed ratio. Then, on each successive mechanical unit gear ratio step shift between gear ratios, the continuously variable unit step ratio shifts through a ratio step equal and opposite to the gear ratio step from each corresponding step-up speed ratio for the lower gear ratio through the stationary reaction speed ratio to the step-down speed ratio for the higher gear ratio to provide the same overall speed ratio before and after the shift. In each intermediate mechanical unit gear ratio, the continuously variable unit progressively continuously changes or shifts through the stationary reaction speed ratio to the step-up speed ratio, the maximum speed ratio, for each mechanical unit gear ratio to provide progressive continuously variable overall ratio change. The stationary reaction speed ratio is substantially the means between the corresponding pairs of step-up and step-down speed ratios. In the highest mechanical unit gear ratio, the continuously variable unit speed ratio changes from the step-down to the stationary reaction speed ratio, the maximum speed ratio in the highest gear ratio in an application, such as a highway vehicle, where the highest gear ratio is used a maximum percent of the driving time. In other applications where the highest ratio is used in a low percent of time and higher ratio coverage is needed, the action phase may be used. The percent power transmitted in the mechanical path, in the starting phase of 1st gear drive increases from zero to a high value, in the accelerating phase of 1st gear and the ratio change portion of higher gears varies between high values and 100% and in the highest speed ratio in the highest gear ratio is always 100%, to provide during normal highway driving operation a very high average percent power transmitted in the mechanical path. The step-up shifts in the mechanical unit and step-down shifts in the continuously variable unit are simultaneously made at shift points having the same hydromechanical efficiency in the lower and the higher ratio for synchronous power or energy transfer shifting providing the same power and speed ratio before and after an upshift.
The transmission control system, having a gear unit portion and a continuously variable unit portion, functions in response to transmission input speed and output speed signals and an engine torque demand signal, such as throttle pedal position, to provide step ratio shifts in the step ratio gear unit and both continuously variable and step ratio changes in the continuously variable unit coordinated for overall continuously variable speed ratio change from zero speed ratio at stall progressively to a maximum speed ratio having all mechanical drive. The gear unit control portion upshifts the gear unit at sequentially higher shift points to higher gear or speed ratios with increasing output speed. The upshift points are at higher output speed with increasing torque demand. The continuously variable portion functions in response to input and output speed and torque demand to vary the continuously variable unit coordinately with gear unit shifting for overall speed ratio change in accordance with an operation program for constant engine speed for optimum economy and performance at proper increasing engine speed values with increasing torque demand with increasing output or vehicle speed.
The continuously variable control portion functions in response to engine or input speed and torque demand, in response to a step-ratio shift at each shift point in the mechanical unit by the gear control portion which tends to change input or engine speed, to cause an equal and opposite step shift in the continuously variable unit speed ratio to provide the same overall speed ratio before and after the simultaneous step shift in both units and, in response to drive in each ratio in the mechanical unit, to cause progressive continuously variable unit speed ratio change at a rate increasing with increasing torque demand and decreasing with increasing gear speed ratio, to provide continuous uniform rate progressively increasing overall speed ratio, with the rate of increase increasing with torque demand. The continuously variable portion torque capacity is limited at and near zero continuously variable unit speed ratio to limit continuously variable unit and overall torque capacity and ratio.
The continuously variable ratio unit is a hydromechanical unit having a planetary gearing portion and a hydrostatic portion. The planetary gearing portion has an input member driven by the transmission input, a reaction member, and an output member driving the multistep ratio gear unit and divides the torque into the mechanical torque path and the hydraulic torque path and transmits torque in the mechanical torque path. The continuously variable bidirectional hydrostatic portion transmits torque in both directions in a continuously variable ratio in the hydraulic torque path between the reaction member and the output member. The mechanical torque path transmits a major portion, and the hydrostatic torque path the minor portion of input torque.
The multistep ratio gear or mechanical unit preferably has powershift gearing having a plurality of gear ratios with steps between the ratios transmitting all torque through a multistep ratio mechanical torque path between the hydromechanical unit output member and the transmission output or load member. The hydromechanical unit provides continuously variable speed ratio change increasing from zero speed ratio in a reaction phase speed ratio range to the speed ratio at zero reaction member speed, the stationary reaction speed ratio, and then in an action phase speed ratio range to higher speed ratios. The hydrostatic portion, in the reaction phase, transmits torque from the reaction member to the output member and loads or brakes the reaction member to decrease reaction member reaction direction speed from a high speed providing zero speed ratio in the hydromechanical unit to zero reaction member speed, or to hold the reaction member stationary relative to ground to provide the stationary reaction speed ratio in the hydromechanical unit to cause the power transmitted in the hydraulic torque path to decrease from 100% to 0%, and in the mechanical torque path to increase from 0% to 100%. Then in the action phase, the hydrostatic transmission transmits torque from the output member to the reaction member to drive the reaction member in the action direction, opposite to the reaction direction, to increase speed ratio from the stationary reaction speed ratio to a maximum speed ratio with power transmitted in the hydraulic torque path increasing from zero to a higher value.
The hydrostatic portion has a reaction hydrostatic converter drive connected to the reaction member of the gearing portion, an output hydrostatic converter drive connected to the output member of the gearing portion and hydromechanical unit and interconnecting power passages. The hydrostatic converters are rotary displacement-type pump-motor units. The reaction and output hydrostatic converters respectively function in the reaction phase as a pump and a motor, and in the action phase as a motor and pump. The hydrostatic converters have variable displacement means to vary the displacement ratio, the ratio of the displacement volume of the output to the reaction hydrostatic converter, from a positive maximum to zero in the reaction phase and from zero to a negative maximum in the action phase, a negative slope variation, preferably in a straight line, relative to increasing output speed. The displacement of the output hydrostatic converter similarly varies from the reaction phase positive maximum to zero for the stationary reaction speed ratio, and then to the action phase negative maximum, with increasing output speed providing increasing hydromechanical unit speed ratio. The reaction hydrostatic converter preferably has a constant positive displacement less than positive maximum displacement of the output hydrostatic converter.
The hydromechanical control portion controls the hydrostatic portion to control the ratios of the hydromechanical unit. The hydromechanical control portion has a power pressure control portion controlling the higher pressure in the power pressure passages to limit torque and control speed and torque ratios in a starting phase, and a displacement control portion to control speed and torque ratios in the accelerating phase in all speed ratios and during each gear ratio shift.
The starting portion of the 1st gear cycle begins at stall--zero speed ratio--where all or 100% power is transmitted through the hydraulic torque path of the hydrostatic portion of the hydromechanical unit, and in series through the multistep ratio gear unit in 1st gear ratio. As the transmission output speed increases and the vehicle begins to move from stall during the 1st gear cycle, the gear unit control portion maintains the gear unit in 1st gear ratio, and the hydromechanical control portion controls the hydrostatic portion to control the hydromechanical transition unit in response to increasing engine speed, output speed and torque demand to progressively increase the speed ratio in a reaction phase from zero speed ratio through a transition speed ratio to the stationary reaction speed ratio, the 100% mechanical torque path power speed ratio, and then to further increase the speed ratio in the action phase to the first step-up speed ratio at the 1st-2nd gear shift speed.
The vehicle starting drive, a low hydromechanical speed ratio range from zero to a transition speed ratio, is controlled by the power passage pressure control portion acting in a power pressure control phase to increase power passage pressure and to exhaust excess fluid as a function of increasing input speed, output speed, and torque demand, with the displacement control portion fixed in the maximum positive displacement ratio and the output hydrostatic converter in maximum positive displacement for motor operation of the output hydrostatic converter to cause pump operation of the reaction hydrostatic converter. Then the hydromechanical speed ratio is progressively increased from the transition speed ratio to the first step-up speed ratio by the displacement control portion in a displacement control phase in which the displacement ratio and the displacement of the output hydrostatic converter are decreased from the positive maximum through zero to the negative maximum, and the power pressure control portion does not regulate or exhaust power passage pressure. The hydromechanical speed ratio is increased from zero to the stationary reaction speed ratio in a reaction phase by reducing reaction direction speed of the reaction member from a maximum to zero in a reaction control phase. The reaction phase includes the power pressure control phase from zero to the transition speed ratio and a displacement control phase portion from the transition to the stationary reaction speed ratio. In the displacement control phase of the reaction phase, the displacement ratio and displacement of the output hydrostatic converter are decreased from a positive maximum to zero to cause the output hydrostatic converter to function as a motor and the reaction hydrostatic converter to function as a pump to brake the reaction member to increase hydromechanical speed ratio from the transition speed ratio to the stationary reaction speed ratio. Then the displacement control phase continues in an action phase in which the displacement control portion further decreases the displacement ratio and the output hydrostatic converter displacement from zero to a negative maximum ratio and displacement for pump operation of the output hydrostatic converter to cause the reaction hydrostatic converter to function as a motor to drive the reaction member in an action direction at speeds increasing from zero to maximum action direction speed to provide hydromechanical speed ratio increasing to the maximum, the first gear step-up speed ratio, at the first second shift point of the mechanical unit.
The combination or product of the first step-up speed ratio and the 1st gear speed ratio provides the overall speed ratio at the first second shift speed. This 1st gear cycle provides continuously progressively variable overall speed ratio change from zero speed ratio to the overall speed ratio at the first second gear shift speed.
The second gear cycle begins with a shift portion at the first second shift speed. The controls step-up shift the gear unit from 1st to 2nd ratio and, in the same time period in response to engine speed, function to maintain constant engine speed and to prevent the normal reduction in engine speed caused by an upshift in a gear unit, by step-down shifting the hydromechanical unit from the first step-up speed ratio to a lower second step-down speed ratio so the overall speed ratio is the same before and after the shift. The second step-down speed ratio, in combination with 2nd gear speed ratio in the gear unit, provides the same, or substantially the same, overall speed ratio at the first second gear shift speed as the first step-up and 1st gear speed ratios. Then, with further increasing engine and output speed in the drive portion of the 2nd gear cycle, the controls retain the multistep ratio gear unit in 2nd gear ratio and provide displacement control operation in the reaction phase and action phase of the hydromechanical unit to progressively continuously increase the hydromechanical unit speed ratio from the second step-down speed ratio to a second step-up speed ratio at the second third gear shift speed to complete the 2nd gear cycle. The product of the second step-up speed ratio and the 2nd gear speed ratio and the third step-down and 3rd gear speed ratios provides the same overall speed ratio at the second third shift speed. There is a similar gear cycle during 3rd gear ratio or all intermediate gear ratio operation of the mechanical unit. In the highest, or 4th gear cycle in this example, the shift portion is the same as in the above-discussed 2nd gear cycle to make the third fourth shift without overall speed ratio change, and in the drive portion the controls maintain the gear unit in 4th speed ratio and control the hydromechanical unit to progressively increase the speed ratio from the 4th step-down ratio up to the stationary reaction speed ratio to provide the maximum overall speed ratio with all power transmitted mechanically.
In the 1st gear cycle, as speed ratio increases from zero through the transition and stationary reaction speed ratios to the step-up speed ratio, the power transmitted by the hydraulic torque path decreases from 100% at stall for high limited torque multiplication, and decreases to a lower value at the transition speed ratio, to zero at the stationary reaction speed ratio, and then increases from zero to a lower value at the step-up speed ratio. In the shift portion of each intermediate and the last, or 4th, gear cycle, and the drive portion of each intermediate gear cycle, the power transmitted by the hydraulic torque path decreases from a lower value to zero and then increases to a similar value, to provide an average power transmitted by the hydraulic torque path of about one-half the lower value. In the drive portion of the highest gear cycle, as the hydromechanical speed ratio progressively increases from the highest gear ratio step-down speed ratio to the zero power stationary reaction speed ratio and remains in this condition, the power transmitted by the hydraulic torque path decreases from the lower value to zero, so that all power is transmitted mechanically in the major portion of highway operation of a vehicle at normal road-load speeds for maximum mechanical efficiency.
The hydromechanical unit displacement-controlled progressive speed ratio ranges employed for acceleration in the intermediate gear shift cycles have a substantially equal portion of reaction phase speed ratio range below or less than the stationary reaction speed ratio and the action phase speed ratio range above or greater than the stationary reaction speed ratio, so the stationary reaction speed ratio is near the mean between the step-down and the step-up speed ratios in each gear ratio, and minimum power is transmitted hydraulically in the intermediate gear cycles for maximum use of the higher efficiency mechanical torque path. When the mechanical unit has conventional speed ratio steps employed in automatic transmissions with a hydrokinetic torque converter, the percent power transmitted in the hydraulic torque path has a maximum value of less than 30% and an average value less than 15%. The mechanical unit may have larger ratio steps to increase the speed ratio range with a lower average percent power in the hydraulic torque path. Thus, in normal vehicle highway driving operation, a very high average percent of mechanical path power is used for a high efficiency drive.
The controls provide coordinated control of the speed ratios of the mechanical and hydromechanical units to provide an overall continuously variable ratio change to control the relationship of engine or transmission input speed and transmission output or vehicle speed in relation to torque demand to provide in accordance with a program for maximum torque multiplication at maximum torque engine speeds to meet high-torque drive requirements and high-torque multiplication at maximum power engine speed for maximum power drive and for programmed decreasing torque ratio for decreasing torque requirements and increasing speed ratio for drive speed requirements providing the engine speed having optimum efficiency generally also the lowest engine speed meeting the drive torque and speed requirements determined by torque demand.
The hydromechanical speed ratio is controlled in the displacement control phase by input speed, which is influenced by mechanical unit speed ratio in relation to output or vehicle speed, and torque demand to provide in each higher mechanical unit speed ratio a hydromechanical unit speed ratio increasing at a lower rate relative to vehicle speed, so the overall speed ratio increases progressively at substantially the same rate. The hydromechanical unit speed ratio decreases with increasing torque demand and the mechanical unit upshifts at higher speeds with increasing torque demand, so the overall speed ratio decreases with increasing torque demand .